Synchronizing rotating bodies



W. s. STEPHENSON ET AL SYNCHRONI ZING ROTATING BODIES Filed March 24, 1924 2 Sheets-Sheet 1 w. s. STEPHENSON ET AL SYNCHRONIZING ROTATING BODIES Filed March 24, 1924 2 Sheets-Sheet 2 Fig.4

3? in 5mm 48 5 um M mm WW 40M g/vavrofis Patented Dec. 30, 1924.

' UNITED STATES I 1,521,205 PATENT OFFICE.

WILLIAM S. STEPHENSON AND GEORGE W. WALTON, OF LONDON, ENGLAND.

SYNCHRONIZING ROTATING BODIES.-

Application field March 24, 1924. Serial Ito. 701,616.

To all whom it may concern:

, Be it known that we, IVILLIAM SAMUEL STEPHENSON and GEORGE WVILLIAM VALTON, both subjects of the King of Great Britain, and residents of Twyford Abbe IVorks, Acton Lane, HarlesdemLondon, J. W. 10, England, have invented certain new and useful Improvements in Synchronizing Rotating Bodies (for which we have filed an application in England dated 30th December, 1922), of which the following is a specification.

This invention relates to means for maintaining two rotating bodies spaced a distance apart in synchronism by the use of wireless or electro-magnetic waves, or by means of currents in telegraph or telephone lines forming what are known as wired wireless systems.

Some progress has been .made with the problems of transmitting pictures or photographs to a distance electrically and of television and in the methods which have been attempted hitherto it has always been neces-.

sary to have a rotating body, usually a drum at the transmitting end and a second rotating body at the receiving end which has to be rotated at the same speed and exactly in step with the first rotating body. In order to maintain these conditions in a satisfactory manner very considerable difficulty has been met and in fact the attainment of these conditions is probably the most diflicult problem to be dealt with satisfactorily in order to solve the problem of television. There are, of course, in addition other fields in which it is necessary to maintain two rotating bodies in synchronism.

According to the present invention the rotating drum or other body at the transmitting end is coupled to or otherwise connected with the rotating member of an alternating current generator and the low frequency potential generated by that generator is employed to modulate energy transmitted in the form of continuous electro-magnetic waves from the transmittingstation. At the receiving station by means of suitable filter circuits the modulating component of the received waves is separated out and is employed to drive an alternating current synchronous motor coupled'with or geared to the rotating drum at the receiving end. It is most convenient to have the drums at both ends actually on the same shafts as the rotating elements ofthe alternating current dynamo-electric machines, but they may be driven through worm gearing or any other form of positive drive. The machine at the transmitting end is preferably a direct current motor of ordinary construction with tappings taken from the armature winding to slip rings; the machine is run as a direct current motor to'drive the rotary drum and is thus practically a rotary converter run up and supplied with power on the direct current side.

Figure 1 is a diagram of connections of one arrangement at the transmitting station in accordance with the present invention;

Figure 2 shows an alternative arrangement at the transmitting station;

Figure 3 is a diagram of connections of one possible arrangement in accordance with .the invention at the receiving station, the

diagram showing by way of example an application of the invention of transmitting pictures by electro-magnetic waves;

Figure 4 shows an alternative arrangement at the receiving station, while Figures 5 and 6 illustrate alternative arrangements at the receiving station in which local power is absorbed in order to avoid the necessity of a large degree of amplification.

In Figure 1, the general mode of connection corresponds with a known form of continuous wave transmitting station having a control valve 1 furnished with reaction coupling 2, 3 between the grid and plate circuits to enable the valve to generate continuous oscillations and to control oscillations in a power valve 4 which are impressed upon the aerial system 5. 6 indicates a low frequency transformer such as might be used in a telephony system for modulating the continuous waves by impressing microphone currents upon the grid circuit of the valve 1. In the present instance, however, the transformer 6 is employed to modulate the continuous wave by means of an alternating current of a frequency corresponding to the speed of the member whose movement is to be reproduced at the receiving end. 7 indicates the shaft of the member therotation of which has to be transmitted faithfully to the receiving station. As already indicated, this may be the shaft of the transmitting drum in a television apparatus, or in a system for transmitting pictures to a distance. This shaft is driven by a dynamoelectric machine 8, 9, which in the example under consideration, is a direct current shunt motor of normal constructon suppiied from direct current mains 10, 11.

owever, tappings from the armature winding are taken to the slip r ngs 9 so that, in fact, this machine is a rotary contion of the machine 8, 9. As illustrated,

the system in Figure 1' transmits a continuous electro-magnetic wave bearing a modulation due to an alternating current of a certain relatively low frequency. How- ,ever, in some applications, it may be needed to transmit signals or indications other than the synchronizing modulation already described. Such signals, as long as they are direct current impulses or of a different frequency from the synchronizing modulation, can be sent and dealt with separately at the receiving station. A method of sending direct current impulses such as might be employed in transmitting pictures is shown diagrammatically. As illustrated a highresistance or leak is included in the grid circuit of the valve 1. A battery 71 is arranged to be connected across the resistance 7 0 when the contacts 72 are closed. The contact 72 may, for example, represent the contacts closed upon the transmitting drum of a picture transmitting apparatus 50 that when the contacts are closed a direct current impulse is placed upon the grid of the valve 1.

Figure 2 shows a different continuous wave transmitting system including two oscillating valves 1, 4 connected in known manner to the aerial system 5, so that the two valves contribute alternate half waves to the continuous wave. In this-case, the source of potential in the plate circuits of the two valves 1 and 4 is an alternating difference of potential derived in know-n manner from alternating current mains 12, 13, through a transformer 6, arranged so that alternately the potential from either half of the secondary winding 73 of the transformer 6 becomes efi'ective in the late circuits of the respective .valves 1, 4. he shaft 7, carrying or rigidly geared to the member whose rotation is to be synchronized, is in this case driven by a synchronous motor 1.4 which receives its supply from the same mains 12, 13. It will be noticed, however, that the ripple eliminator usually necessary for such systems supplied from alternating current mains is omitted, so that the electro-magnetic wave transmitted will be a continuous wave modulated with a'ripple corresponding to the frequency of the supply mains and therefore correiponding also to the speed of the shaft 7. n this system direct current impulses might be sent in a manner similar to that described with reference to Figure 1. In Figure 2 a. high resistance or leak 70 is shown included in the conductor common to the grid circuit of both the valves 1 and 4 and in a similar way a battery 71 is arranged to be connected. across the resistance 70 when the contacts 72 are closed. A high frequency by-passing condenser 74 is also shown included as in Figure 1.

Figure 3 shows One form of connections at a receiving station and, as'already mentioned, it is illustrated in a rudimentary way as applied to the receiving of pictures transmitted electrically. Any form of receiver for continuous waves may be employed and in this figure it is indicated diagrammatically by a valve 15 furnished with reaction coupling 16, 17 and this may be preceded or followed by severalstages of thermionic valve amplification. An oscillatory circuit 18, 19 connected between the plate and filament of the valve 15 is tuned as a trap. or filter for the low frequency of themodulation, that is to say, it consists of an inductance 18 in parallel with a condenser 19' tuned to form a circuitof infinite impedance to the low frequency of the modulation. The result is. that the low fre-'- quency impulses in the platecircuit of the although the invention is in no way limited to this, these direct current impulses. are caused to control a source of illumination 24 for reproducing the pictures transmitted. This source is an incandescent lamp and is connected in series with a lighting battery 25 when the relay 23 closes its contacts.

circuit 32, 33 tuned to the low frequency of the modulation and the other side'of this circuit is connected to the mid-point 34 of the resistance 31. The inductance 32 of the oscillatory circuit 32, 33 is coupled to a secondary winding 35 from which energy is taken to an alternating current cynchronous motor 36. This motor carries on its shaft or is rigidly geared to the member at the receiving station which is kept in synchronism with the rotating member at the transmitting station and may be the rotating drum or other similar part of the receiving apparatus of asystem for sending pictures electrically, in the particular example taken.

When the tongue 26 is making contact with the right hand butt 28, as illustrated in Figure 3, the current flows from the positive main 29 through the butt 28, the tongue 26, downwards through, the winding 32 to the point 34, through the left-hand half of the resistance 31 back to the negative main 30. lVhen the tongue 26 passes over into contact with the butt 27 on the other hand, the current flows from the main 29 through the right-hand half of resistance 31 up wards through the winding 32, \the tongue 26, butt 27 to the negative main '30. Thus the current flows from the direct current mains 29, alternately upwards and downwards in the winding 32 at a frequency corresponding to that of the synchronizing modulation. These pulses cause an oscillatory current of the same frequency to be setup in the circuit 32, 33 which in its turn induces a current of that frequency in the secondary winding 35 so that the motor 36 is kept strictly in synchronism with the shaft 7 at the transmitting station.

Figure 4 shows a modified receiving system. The valve 15 corresponds exactly to the valve 15 in Figure 3 and may correspond to several stages of thermionic valve amplification. The plate circuit of valve 15 is shown to have two branchesone including a condenser 37 to prevent the passage of the direct component of the plate current of valve 15 and also including the primary winding 38 of a transformer; in the other branch of the plate circuit there is one seeondary winding 39 of the transformer provided with sufficient turns to have a terminal voltage equal to the alternating current voltage applied to the primary winding38. The second branch also includes a condenser 40 equal to the condenser 37 and a high resistance 41. The junction point 42 between the primary winding 38 and the secondary winding 39 is connected direct to the filament 43 of an additional valve 44. The mid point of the resistance 41 is connected to the grid of the valve 44.

It is clear that the filament 43 is connectedto the junction point 42 and that between this connection and the left hand end of the resistance 41, there is the primary winding 38 and the condenser 37 while between this connection and the right hand end of the resistance 41 there is the secondary winding 39 and the condenser 40. Consequently the alternating current differences of potential due to the frequency of the modulation at the two ends of the resistance 41 are equal and of opposite sign with respect to the potential of the filament 43. The grid 45, however. receives the potential of the mid point of the resistance 41. Therefore, there isno difference of potential due to the alternating current of the frequency of the modulation between the filament 43 and the grid 45. Thus there is no alternating current of this frequency in the plate circuit of the valve 44 and signals or indications distinct from the modulated alternating current only can betaken off from the terminals 46, 47 which therefore correspond exactly to the terminals 46, 47 in Figure 3. The additional secondary winding 48 coupled with the primary winding 38 receives an alternating current of a frequency of the modulation and this can be taken off from the terminals 49, 50 for driving a synchronous 'motor or for other alternating current purposes either after or before further amplification. Thus, the terminals 49, 50 corre spond exactly to the terminals 49, 50 in Figure 3.

Tn Figure 5 is shown an arrangement at the receiving station enabling power to be taken from a local source comprising direct current mains 51, 52. The valve 15 with reaction coupling 16, 17 corresponds to the valve similarly indicated in Figures 3 and 4. Therefore, in its plate circuitit has a low frequency component of the frequency of the modulation. However, a second low frequency component is impressed upon it and is conveniently of somewhat a different frequency from that of the modulation. This is obtained from the machine 53, 54 which represents either a rotary converter supplied on the direct-current side from the mains 51, 52, or a small direct current motor 53 driving a small alternator 54. The resulting alternating current is supplied to the 1 primary winding 55'of a low frequency transformer also coupled with a coil 56 in the plate circuit of the valve 15. The frequency impressed upon the coil 55 cannot, of course, be very easily maintained exactly equal to that of the modulation dependent on the transmitting station, but for convenience it is made fairly close to'that frequency. In the plate circuit of the valve 15 there are therefore two components of low frequency, one due to the modulation from the transmitting station, the other due to the current 55. It can easily be shown that there is a resulting component of a frequency mid-way between these two frequencies and a current of this frequency is taken off by means of the transformer 57 58 and supplied to the synchronous motor 59. The latter ,is carried by a sleeve 60 attain some speed frictionall loose on the shaft 61 of the machine 53, 54. Therefore, when the machine 53, 54 is started up, the rotor of the machine 59 will as it is not loaded, but its ultimate spee will be govern'ed by the frequency taken from coil 58. The shaft 61 has secured to its righthand end, a sun wheel 62 and the sleeve carries the planet carrier 63 of a differential gear. The planet pinions 64 mesh with a wheel 65 driving the shaft 66 of the member which runs in synchronism with the rotating member at the transmittin station.

If m is-the frequency of mo ulation and Z is the frequency obtained from the machine 54, the frequency from coil 58 is Therefore, the sun wheel 62 is rotated at a speed proportional to Z; the planet carrier 63 is turned at a speed proportional to and the wheel 65 and the shaft 66 are therefore driven at a speed proportional to' synchronous speed corresponding to the frequencyof modulation, for example, in the same wayas the motor 36 in Figure 3. On the same shaft as the motor 36, there is the v armature 67 of a direct current series motor.

. increasing y the tendency of the motor 36 the receiving station.

to remainin synchronism. The shaft 66, therefore, carries or is rigidly geared to the member'which is driven in synchronism at,

Other formsof tuned signalling usually known as f wired wireless systems may be ap lied to the present invention without any d culty. Any of the transmittin ceivmg arrangements hereinbefore (f. 01 reescribed and illustrated for wireless transmission may be employed for such wired wireless applications. The connections will be as illustrated except that the transmitting and receiving aerials will be replaced by the-line servin to guide the electro-magnetic waves.

Havln'g thus described our invention what we claim as new and desire to secure by Letters Patent is 1. A system for maintaining in synchronous movement two spa ced movablemembers of an apparatus of a type adaptedfor use in the representation of pictures at a distance, television or like transmission of intelligence, one of said members being a transmitting member and the second of said members being a receiving member, comprising in combination a transmitter and receiver of undamped electro-ma netic waves,

a machine for generating low requency al-.

ternating currents driven in synchronism with one of said members and coupled to said transmitter of undamped waves so. as

to modulate the wave transmitted, a filter circuit connected to said receiver, of undamped waves so as to filter out the alternating current received due to the low frequency modulation, -an alternating current motor connected to said receiver to be controlled by the alternating current filtered out and mechanically connected to drive said second member.

2. A system for maintaining in synchronous rotation two spaced rotating members of an apparatus of a type adapted for use in the representation of pictures at a distance, television or like transmission of intelligence, one of said members being a transmitting member and the second of said members be1ng a receiving member, comprising in combination a vacuum tube transmitter of undamped electro-magnetic waves and includin an oscillating vacuum tube with feed bac coupling and with input and output circuits, a machine driven from one of said rotating members and adapted to generate low frequency alternating currents and coupled with the in ut circuit of said oscillating tube to modu ate the undampedwave transmitted at the said low fre uency a vacuum tube receiver for the un amped electro-magnetic waves including a vacuum tube with input and output circuits, a circuit tuned to the low frequency modulation and a circuit untuned to the ow frequency of said modulation both connected to the output circuit of said last-mentioned vacuum tube, a synchronous alternating current electric motor, connections between said motor and said untuned circuit enabling the low frequency alternating current in the latter to control said motor said motor also bein mechanically coupled to drive said secon rotating member. 7 3. An apparatus for a rotating iso ' bers of an apparatus of a type adapted for body in synchronism with the modulation of a received undamped electro-magnetic wave, comprising in combination a vacuum tube receiver with input and output circuits, a pair of branches included in said output circuit and consisting respectively of a branch tuned to said modulation and a branch not tuned to said modulation so that the received component due to said modulation is separated and caused to flow in said second-named branch, a control apparatus regulated by said low frequency current, a synchronous alternating current motor connected to said control apparatus and driving the rotating body, a series direct current motor coupled with said synchronous alternating current motor and a local source of direct current supplying said direct current motor and tending to rotate the latter at a speed somewhat higher than the synchronous speed of said alternating current motor.

4. A method of maintaining in synchronism by means of an electro-magnetic wave signaling system two spaced movable memuse'm the representation of pictures at a distance, television or like transmissionof intelligence, one of said members being a transmitting member and the second of said members being a receiving member, said method consisting in transmitting an undamped electro-magnetic wave, modulating said wave in synchronism with one of the movable members, receiving said modulated undamped wave, filtering out the low frequency received current due to said modulation and supplying said filtered low frequency alternating current to an alternating current motor driving the second movable member.

5 A method of maintaining in synchronism by means of 'an electro-magnet 'wave signaling system two spaced rotating members of an apparatus of a type adapted for use in the representation of pictures at a distance, television or like transmission of intelligence, one of said members being a transmittin member and the second of said members being a receiving member and said members driving and being driven by, re spectively, alternating-current electrical machines, said inethod consisting in transmitting an undamped elctro-ma-gnetic wave, modulating said wave by means of a low frequency alternating current supplied by the electrical machine driven by one of said members, receiving said modulated undamped electro-magnetic wave, filtering out the received low frequency alternating current due to the modulation and supplying said filtered alternating current to the electrical machine driving the second of said rotating members.

6. A method of maintaining in synchronism by means of an electro-magnetic wave signaling system two spaced rotating members of an apparatus of a type adapted for use in the representation of pictures at a distance, television or like transmission of intelligence, one of said members being a transmitting member and the second of said members being a receiving member and said members driving and being driven by, respectively, alternating-current electrical machines, said method consisting in transmitting an undamped electro-magnetic wave, modulating said wave by means of a low frequency alternating current supplied by the electrical machine driven by one-of said members, receiving said modulated undamped electro-magnetic wave, amplifying the received current due to said undamped electro-magnetic wave, filtering out the received low' frequency alternating current due to the modulation and supplying said filtered alternating current to the electrical machine driving the second of said rotating members.

7. A system for the transmission of representations comprising in combination a vacuum tube transmitter of undamped electro-magnetic waves including a vacuum tube with input and output circuits, a rotating transmitting drum, contact members cor responding to a representation to be transmitted carried by said drum, a low frequency alternating current generator mechanically coupled to said drum and electrically coupled to the input circuit of said tube to impose upon the transmitted wave a low frequency modulation, a source of direct current intermittently coupled with the input circuit of said tube by said contact members rendered operative in accordance with said representation to impose a unidirectional modulation upon the transmitted wave, a vacuum tube receiver for the electro-magnetic wave including a vacuum tube with input and output circuits, a pair of branches connected to the output circuit of said last-named tube, one tuned to the frequency of the alternating current due to the modulation and the other untuned, a receiving drum, an alternating current syn chronous motor coupled therewith and connections between said motor and said untuned branch enabling the alternating currents received due to the modulation to control the speed of said motor and said re ceiving drum, a source of illumination, a switch mechanism controlling the circuit of said source of illumination and itself controlled by the direct current impulses in said untuned branch.

8. An apparatus for transmitting and receiving an undamped electro-magnetic Wave modulated in accordance with the movement of a rotating body comprising in combination a vacuum tube transmitter including a vacuum tube 'vvith input and output circuits, :1. direct current motor mechan-- said slip rings, a receiver of undamped elec-' tro-magnetic waves, a filter circuit connected to said receiver of undamped waves so as" to separate out the low-frequency alternating current received, and an alternatingcurrent motor connected to said receiver to be controlled by the alternating current separated out and mechanically connected 15 to drive a second moving body.

In witness whereof We hereunto subscribe our names this 5th day of March, A. D. 1924:.

W. S. STEPHENSON. G. W. WALTON. 

